NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

Panel on Research Methodologies and Statistical Approaches to Understanding Driver Fatigue Factors in Motor Carrier Safety and Driver Health; Committee on National Statistics; Board on Human-Systems Integration; Division of Behavioral and Social Sciences and Education; Transportation Research Board; National Academies of Sciences, Engineering, and Medicine. Commercial Motor Vehicle Driver Fatigue, Long-Term Health, and Highway Safety: Research Needs. Washington (DC): National Academies Press (US); 2016 Aug 12.

Cover of Commercial Motor Vehicle Driver Fatigue, Long-Term Health, and Highway Safety

Commercial Motor Vehicle Driver Fatigue, Long-Term Health, and Highway Safety: Research Needs.

Show details

4Hours-of-Service Regulations

An important way in which the Federal Motor Carrier Safety Administration (FMCSA) tries to reduce crashes, injuries, and fatalities involving large trucks and buses is by issuing and enforcing hours-of-service (HOS) regulations for property- and passenger-carrying commercial motor vehicle (CMV) drivers in the United States. HOS regulations specify the maximum number of hours that truck and bus drivers are allowed to work in a 24-hour day or a 7-day week. The hope is that limiting the number of hours that CMV drivers are allowed to be on duty gives them the time to acquire sufficient rest, and by doing so reduces fatigue-related crashes. The regulations serve two purposes: (1) they limit time on task, and (2) they allow for periods of rest and sleep. This chapter provides a brief description of HOS regulations in the United States. It also describes HOS regulations in Canada and Mexico, since trucks and buses from these countries routinely enter the United States and vice versa, and HOS regulations in these countries can therefore be compared with those in the United States.


The first HOS regulations for interstate commercial drivers were issued in 1938 by the Interstate Commerce Commission (ICC), which was then the relevant regulatory agency. The ICC issued the regulations because it understood that the industry's operations generated safety concerns among the public, and the existing regulatory framework was falling short in addressing those concerns. The ICC subsequently modified its HOS regulations in 1939, 1962, and 1963, after which the regulations remained unchanged until 2003. In 1995, the ICC was abolished, and in the same act, Congress directed the Federal Highway Administration (FHWA) to establish new regulations incorporating the latest scientific knowledge about human fatigue and alertness.1 The 1999 Motor Carrier Safety Improvement Act led to the creation of FMCSA and established safety as the new agency's highest priority. In 2003, FMCSA published new regulations that reflected the congressional directive, which were then revised in 2011. The regulations specify maximum on-duty time, minimum off-duty time, and maximum total driving hours. They also outline the manner in which a driver can utilize off-duty time to incorporate rest, which includes breaks from work and time for sleep.


Duty Cycle

Duty cycle, in this context, refers to a day-like period of maximum on-duty time followed by minimum off-duty time, which may or may not sum to 24 hours. Thus, for example, if the maximum on-duty time were 12 hours and the minimum off-duty time were 10 hours, a “day” could restart after 22 hours, and a driver could do this until weekly limits had been reached. When the duty cycle differs from 24 hours, there is clearly some misalignment with the driver 's circadian clock. A duty cycle differed from 24 hours until recently, when, to provide for circadian alignment, FMCSA set it to 24 hours. The term is sometimes also applied to limitations on the number of hours that can be spent driving in a 7- or 8-day period.

On-Duty Time

On-duty time refers to the time during which the driver is working, which encompasses driving, loading, and unloading. The HOS regulations set limits on on-duty and driving time:

  • On-duty limit refers to the maximum amount of total duty time in a 24-hour duty cycle and a 7-day period that is allowed.
  • Driving limit is the maximum amount of total driving time between two off-duty periods that is allowed.

Off-Duty Time

Off-duty time refers to the time during which the driver is not performing any work related to his or her job:

  • Off-duty limit refers to the minimum number of hours that a driver must be off duty in a 24-hour duty cycle given that the driver is on duty for the maximum number of hours allowed by the HOS regulations.
  • Rest breaks consist of the off-duty time that a driver utilizes for purposes of resting. In the United States, a rest break is a 30-minute period of time.
  • Sleeper berth provision: If a truck has a sleeper berth (which should meet safety requirements), a driver can use the sleeper berth to rest during the off-duty period. The sleeper berth provision under the HOS regulations allows drivers some flexibility in how they utilize their off-duty time.2

In addition, the HOS regulations include a restart provision that requires drivers who drive the maximum number of allowable hours to restart their weekly duty cycle after being off duty for a certain number of hours.


Table 4-1 summarizes the HOS regulations enforced by the ICC until 1995 and then by FMCSA starting in 1999.

TABLE 4-1. Hours-of-Service Regulations.


Hours-of-Service Regulations.

The ICC and FMCSA also placed limitations on the maximum number of hours a CMV driver is allowed to drive in a weekly duty cycle. The HOS regulations from 1938 to 1962 allowed drivers to drive for 60 hours in a 7-day period or 70 hours in an 8-day period. The 2003 HOS regulations increased the maximum driving hours to 77 hours in a 7-day period or 88 hours in an 8-day period, while the 2011 regulations reverted back to 60 or 70 hours in a 7- or 8-day period, respectively.

Table 4-1 reveals that there has been little change in the distribution of off-duty minimums and on-duty maximums in almost 80 years. The regulations of 1962, 1963, and 2003 required drivers to work in a cycle of work (driving time) and rest (off duty) that was less than 24 hours (i.e., an 18-hour rotation in 1962-1963 and a 21-hour rotation in 2003). Such duty cycles ignored the nondriving tasks performed by drivers while on duty, and as noted above, they were not aligned with the circadian (24-hour) biological cycle regulating sleep and alertness. Between 1963 and 2003, FHWA issued two notices of proposed rulemaking, one in 1978 and the other in 1992, to change the HOS regulations. However, neither of those proposals was finalized.

FMCSA's 2003 rulemaking took into account the research done on the human need for recovery sleep by introducing the restart provision, which, as noted above, allowed drivers to reset their weekly duty cycle. These two changes in the 2003 HOS rules, which lengthened the allowable number of hours per week to greater than 60 and at the same time instituted a restart provision, are somewhat at cross-purposes, since one change reduces the potential off-duty time for workdays, while the other maintains it for nonworkdays. FMCSA's 2011 rulemaking changed the duty cycle to 24 hours to be consistent with the circadian cycle. It also modified the 34-hour restart period to include two consecutive nighttime periods (encompassing the time interval from 1 AM to 5 AM each night) that a driver was off duty between two weekly duty cycles. This was done to increase driver sleep time during circadian and environmental night. The 2011 rulemaking also rescinded the flexibility to split sleep under the sleeper birth provision so as to discourage drivers from experiencing irregular and shorter periods of sleep. FMCSA indicated that the new rules “moved drivers toward a work-rest schedule that more closely matched the natural circadian cycle of 24 hours and gave drivers the opportunity to obtain the 7 to 8 hours of uninterrupted sleep per day that most adults need,” which would be concordant with the discussion of driver fatigue and human physiology in Chapters 1 and 3.

It is obvious from Table 4-1 that truck and bus drivers need to manage their time and track their activities to avoid violating the HOS regulations. The regulations are promulgated for safety purposes and are applied uniformly to both the truck and bus industries. However, the two industries are highly segmented and heterogeneous in terms of the demands placed on their drivers (see Chapter 2), so the impact of the regulations depends on the type of trucking or busing in which a driver is engaged. Therefore, to understand the linkages among driving times, driver fatigue, and crash risk, both current HOS regulations and drivers' typical driving schedules are among the many factors that need to be accounted for. Part III of this report describes the research that has been conducted to investigate those linkages.


Regulations for work and rest hours for truck and bus drivers have also been promulgated by Canada and Mexico. The combined trade relationship among the United States, Canada, and Mexico amounts to $1.4 trillion annually, making trucking a major contributor to commerce among the three countries. And just as the movement of goods is facilitated by trucks, the mobility of persons is facilitated by bus networks that enable travel for people from the three countries.3 The regulations for Canada and Mexico, as well as Australia and the European Union, are summarized in Table 4-2.

TABLE 4-2. Hours-of-Service Regulations in Other Countries.


Hours-of-Service Regulations in Other Countries.



Interstate Commerce Commission Termination Act. See http://www​​/pkg/PLAW-104publ88​/html/PLAW-104publ88.htm [March 2016].


For more details on the sleeper berth provision, see https://www​​.gov/regulations/title49/section/393.76 [March 2016].


Annual data on Border Crossing/Entry of Trucks and Buses from Canada and Mexico, U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, based on data from the Department of Homeland Security, U.S. Customs and Border Protection, Office of Field Operations.

Copyright 2016 by the National Academy of Sciences. All rights reserved.
Bookshelf ID: NBK384967


  • PubReader
  • Print View
  • Cite this Page
  • PDF version of this title (1.5M)

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...